The objective of the proposed research is to investigate the effects of nonparental infant day care on socio-emotional and cognitive development in infants and preschoolers. This will entail a prospective longitudinal study of 220 mothers and their firstborn children, beginning shortly after the child's birth and continuing until the child is 42 months of age. Mothers will be interviewed 2 to 6 weeks postpartum; mothers and children will be seen again when the child is 3, 15, 18, 24, 36, and 42 months of age. Information about the child's nonparental care will be collected every 6 months. Because of the significance of nonparental infant care for the development of secure mother-infant relationships, concepts from attachment theory will be used to guide the investigation. A framework is presented in which to consider the contributions of variables often associated with nonparental care. These include (1) differences in employed and nonemployed mothers' attitudes toward separation and attachment, views of their infants, and life circumstances, (2) differences in employed and nonemployed mother's interactions with their infants, and (3) specific features of the child's experience in nonparental care. Maternal life circumstances to be examined include role preference and role congruence, social support, stress, maternal coping and marital adjustment. Not only will the separate contributions of each of these variables be considered, but also to be assessed are how these variables operate in combination and over time to influence child developmental outcome. In addition, special attention will be given to the developmental timing of the mother's return to employment as it might moderate the effects of nonparental care. This information will be useful to individual families, child care professionals, developmental psychologists, and public policy planners in planning nonparental day care for infants.